With the continuous progress of technology, the demand for liquid crystal display apparatus grows increasingly. Thin film transistor liquid crystal displays (TFT-LCDs) also have become the dominant display devices used for mobile phones, flat panel computers and the like products. In addition, the demands for high color quality, high contrast ratio, wide viewing angle, quick response speed and low power consumption become increasingly widespread, and organic light emitting diode (OLED) displays enter the market gradually.
At present, it is the amorphous silicon thin film field effect transistor that has been commonly applied to the liquid crystal display industry with mature process. But, due to its low mobility, big size and poor stability, it is difficult to apply such transistor to high definition TFT-LCDs and current-driven type TFT-OLEDs. With higher mobility (usually hundreds times higher than amorphous silicon) and better stability, low temperature polysilicon thin film field effect transistors (LTPS-TFTs) can provide higher drive capacity with a smaller device size and can be applied to high definition TFT-LCDs and current-driven type TFT-OLEDs. Furthermore, the LTPS-TFT technology can integrate the integrated circuits originally provided at the periphery of the display panel directly onto the glass substrate of the display panel, whereby the panel becomes lighter and easier to carry and the performance of the display is improved with less peripheral components and lower costs.
At present, the LTPS-TFT has higher contents of impurity in its active layer, so the leakage current in the active layer is relatively great, which directly affects the switching characteristics of the display device using this kind of thin film transistors. Therefore, it has become the focus of attention to prepare thin film transistors with lower contents of impurity at a low temperature.